The temporal and spatial distribution of boats, harbour seals Phoca vitulina and moulting ducks Somaleria mollissima, Tadorna tadorna have been registered by aerial surveys covering the entire Wadden Sea region of Schleswig-Holstein between May 1987 and September 1990. A prominent temporal overlap of the sensitlve periods for seals (pup-rearing) and ducks (being flightless during moult), on the one hand, and the occurrence of high numbers of boats on the other hand was found. During the 'boating season' between May and October more than 60% of the boating traffic is due to leisure boats, whereas 'outside the season' only 10% of all boats belong to that category. A well defined spatial segregation of areas with high boating traffic and important areas for seals and moulting ducks is evident. The lack of boating activities in the latter areas provides good conditions for the development of the species concerned. Disturbances of seals have still been observed in the bordering buffer zones. 75% of these disturbances are caused by boats, which indicates that boating is a factor influencing the spatial distribution of these sensitive species. Besides other factors, whether boating is an important factor affecting the population development of seals and moulting ducks in the Wadden Sea is discussed. Some recommendations for boating traffic (e.g. the creation of 'zero-use regions') are given. Activities involving leisure boats should not take place in these highly protected areas.